Flat light source

ABSTRACT

A flat light source having a front plate and a rear part. The front plate is held at a distance from the rear part by spacers. A gaseous filling which is under a pressure lower than the ambient atmospheric pressure is introduced into the intermediate space between the front plate and rear part, and the front plate is of a glass material. To be able to produce flat light sources of this type which have a low intrinsic weight, according to this invention the front plate and/or the rear part can be configured as an at least partly thermally or chemically tempered glass pane or the front plate and/or the rear part can be configured as a glass pane which at least in areas is coated with ductile polymer material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a large-area radiator with a front pane and arear element, wherein the front pane is kept apart from the rear elementby spacer elements, a gaseous filler is introduced into the spacebetween the front pane and the rear element and is at a lesser pressurethan the pressure of the surrounding atmosphere, and the front pane ismade of a glass material.

2. Description of Related Art

Transmissive LCDs require background illumination by a strong light ofhomogeneous luminance, reduced thickness, low rate of breakage duringassembly and handling, and with a great strength over time. Gasdischarge lamps with a filling of a noble gas at underpressure meet therequirements of homogeneous luminance and low heat emission. These lampscan also be designed as large-area radiators.

The main mechanical components of such large-area radiators are thefront and rear pane and spacer elements for keeping the front and rearpanes apart. Front and rear panes made of glass are preferred. It isknown to provide rear panes made of glass with reflecting coatings, orfoils.

Large-area radiators are known, wherein the discharge current flowsthrough “folded” channels between the front and rear panes, whichrequires an operating voltage of several hundred Volts (CompanyPublication “Flat Candle Backlight Products for 4″ Diagonal LCD”).Large-area radiators are also known, in which the current flows directlyfrom the rear to the front pane. Such large-area radiators are operatedin connection with LCD applications with operating voltages of onlyapproximately 10 V.

A considerable disadvantage of large-area radiators with anunderpressure filling is the great thickness and large weight. Thethickness is the result of the minimum discharge distance and of thethickness of the glass panes for the front and rear panes. The panethickness is the result of strength requirements.

Large-area radiators with front and rear panes of approximately 2.5 mmthickness, which are maintained at an essentially even distance of 40 to50 mm by spacer elements, are known. FIG. 1 shows a section in aperspective view, taken through a known large-area radiator, in whichthe front and rear pane and parallel, continuous, strip-shaped spacerelements are shown. It is known that when employing thinner glass panesfor the front and rear pane, for example for weight-saving or forreducing the thickness of the large-area radiator, the followingproblems occur: too large mechanical stresses in the panes; too greatbending of the panes between spacer elements; and buckling, tipping overor tearing off of the spacer elements.

The mechanical stresses in the panes because of the exterior pressureare considered to be a main problem. The tensile stress at the exteriorsurfaces of the pane is on a scale of approximately σ×a(w/t)², wherein tidentifies the pane thickness and w the distance between the spacerelements. When the pane thickness is reduced, it is also necessary toreduce the distance between the spacer elements. It is assumed that witha pane thickness t=2.5 mm, a distance between the spacer elements of atleast w=40 to 50 mm is required to keep the tensile stress at theexterior surface of the panes below approximately 10 MPa (expectedfatigue strength of class). At a pane thickness of 1 mm, a distancebetween the spacer elements of less than 20 mm would therefore berequired. This results in an increased production outlay and a reductionof the light yield because of the many spacer elements. This assumptionhas prevented the production of large-area radiators with thinner frontand rear panes, or with a greater distance between the spacer elements.

SUMMARY OF THE INVENTION

It is one object of this invention to achieve a weight reduction of alarge-area radiator of the type mentioned above.

This object of this invention is attained with a front pane and/or arear pane that are embodied as glass panes, which are at least partiallythermally or chemically tempered.

With thermally or chemically tempered glass panes it is possible toachieve considerably greater spacer element distances than with knownlarge-area radiators. Table 1 shows what maximum distance can beobtained for the spacer elements w as a function of the pane thicknesst, and what surface pressure tempering must be achieved in the glasspanes at least (σ_(vtmin)).

TABLE 1 without coating with coating t (mm) w (mm) σ_(v1min) (Mpa)W_(max) (mm) σ_(v1min) (MPa) 2.1 105 120 120 120 1.9 85 100 100 100 1.768 80 82 80 1.5 52 60 65 60

Tempering of more than 100 MPa in thin glass panes can only be achievedwith high-stress glass (thermal expansion coefficient_(σ20,300)>7×10⁻⁶1/° C.) or with glass with a high T_(G)(T_(G)>550° C.;where T_(G) is the temperature at which the viscosity of the glass is10^(13.6) dPa). The use of glass with a high T_(G) has a furtheradvantage that it is possible to subject the large-area radiators tohigh temperatures during the manufacturing process. Therefore glass witha high T_(G) is preferred. But the thermal tempering of thin glass panesis still very expensive.

For panes with low stress, or for panes of a thickness of less than 1.5mm, thermal tempering shows hardly positive effects. Therefore chemicaltempering with known methods is preferred.

The combination of chemical tempering and coating with ductile polymerlayers here leads to a further increase in strength. Coating must beperformed after tempering.

With chemically tempered glass it is possible to achieve considerablygreater distances between the spacer elements than with the knownlarge-area radiators, along with a sufficient strength of the large-arearadiators. Table 2 shows the distance w between spacer elements whichcan be achieved as a function of the pane thickness t, and what surfacepressure tempering must be achieved in the glass panes at least(σ_(vtmin)).

TABLE 2 without coating with coating t (mm) w (mm) σ_(v1min) (MPa)W_(max) (mm) σ_(v1min) (MPa) 1.5 95 200 105 200 1.3 81 200 89 200 1.1 70200 76 200 0.9 55 200 61 200 0.7 42 180 46 180 0.5 28 160 32 160

It was found that the strength of the large-area radiators can beconsiderably increased if the stability under load of the spacerelements is increased by using wavy spacer elements instead of straightspacer elements.

An object of this invention is also achieved with the front pane and/orthe rear element embodied as glass panes, which at least partially havea coating of a ductile polymer material.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of this invention are better understood when thisspecification is read in view of the drawings, wherein:

FIG. 1 is a sectional perspective view of a large-area radiator havingparallel strip-shaped spacer elements;

FIG. 2 is a schematic top view and partial sectional view of alarge-area radiator having parallel strip-shaped spacer elements;

FIG. 3 is a schematic top view and partial sectional view of alarge-area radiator having segmented spacer elements;

FIG. 4 is a schematic top view and partial sectional view of alarge-area radiator having spot spacer elements; and

FIG. 5 is a schematic top view and partial sectional view of alarge-area radiator having wavy spacer elements.

DESCRIPTION OF PREFERRED EMBODIMENTS

Large-area radiators with a rectangular base and of an even thicknessare used to describe this invention, however, the teaching in accordancewith this invention can also be applied to other shapes of large-arearadiators. Therefore those are made a part of this invention.

Parallel, strip-like spacer elements, which continuously extend parallelwith an edge of the large-area radiator (FIG. 2), are used to describethis invention. However, the teaching in accordance with this inventioncan also be applied to any other designs, in particular segmented spacerelements (FIG. 3), and spot spacer elements (FIG. 4), or wavy spacerelements (FIG. 5), which are a part of this invention.

It was discovered that a sufficient strength of large-area radiatorscould also be achieved with front and rear panes of glass of a thicknessof less than 2.5 mm, if the glass panes are laminated with plasticcoatings.

Tests have shown that with laminating the exterior of the glass panes,used as front and rear panes, with thin, ductile polymer films, asufficient surface strength of the large-area; radiators is achieved.Suitable for this are thin coatings of silicon, polyurethane or polymersfrom the group of ormoceres. Because of their high temperatureresistance (up to 200° C.) and great resistance to many organic solventsand aqueous solutions, silicon coatings are preferred.

The polymer films already become effective at coating thicknessesstarting at approximately 6 μm. The stability increasing effects of thecoatings basically increase with increasing thickness. However, startingat a thickness of 50 μm this increase is no longer significant. Thethickness range between 6 to 50 μm is preferred, because then theelasticity of the bond is little reduced and the shrinkage of thepolymer films leads to only small stresses in the glass panes. However,the application of thicker coatings up to approximately 200 μm can beuseful for manufacturing reasons.

It is possible to employ primers for improving the adherence of themainly homopolar polymers on the polar glass surface which, by areactive bond of OH groups on the glass surface with their homopolarside chains, provide a homopolar glass surface with good adhesiveproperties for homopolar organic polymers. Dimethoxydimethyx silane orhexamethyl disilazane, for example, are suitable primers.

The stability-increasing effect of the polymer coatings actually is astability conservation. The coatings prevent the creation ofstability-reducing micro-defects in the surface of the glass panesduring transport, assembly or handling of the glass panes. This effecttherefore is particularly developed when the coatings are applied early,preferably immediately following the drawing of the glass panes, andeven more preferred prior to cutting the glass panes, for example forfabricating the panes in the size of large-area radiators.

With the above described glass panes it is possible to achieveconsiderably greater distances between spacer elements than with theknown large-area radiators, without their strength being reduced. Table3 shows, by way of example, which distances w between spacer elementscan be achieved as a function of the pane thickness t.

TABLE 3 t (mm) w (mm) 2.1 75 1.9 65 1.7 54 1.5 48 1.3 37 1.1 31 0.9 250.7 20

An advantageous variation can result if the polymer coating is appliedat a temperature above the operating temperature of the large-arearadiator. With this the polymer coating on the pane is under permanentcompressive strain and is therefore scratch-proof.

Coatings with polymers have one disadvantage that the coated glass panesmay not be exposed to high temperatures during subsequent thermaltreatment. The temperature must remain clearly below 200° C. as a rule.This limitation is unacceptable if, for example, the panes must besoldered while mounting the large-area radiator, or if gettering must beperformed on mounted large-area radiators.

In this case, the panes can be advantageously sealed with a removableprotective film immediately following their production. This temporaryprotective film is washed off prior to the respective temperaturetreatment. Thereafter, another temporary sealing takes place, ifrequired, or there is the immediate application of the permanentcoatings in accordance with this invention.

Tests show that it is possible to create a thermal tempering of panesstarting from a thickness of 1.5 mm by strongly blowing cold air againstthem or dipping them into oil, or oil-covered water, which considerablyincreases the stability of the large-area radiators. Thermal temperingshould take place after cutting the glass panes, for example forfabricating the panes in the size of large-area radiators.

The combination of thermal tempering and coating with ductile polymerlayers results in a further increase of stability. Coating must occurafter tempering.

This invention is explained in greater detail in view of twoembodiments:

Embodiment 1

The rear pane of a large-area radiator, which itself is finished andcapable of functioning, is sprayed with a thin coat of a two-componentsilicon polymer after the last baking process, so that a continuouswetting layer is created. The layer is then polymerized. The amount ofsilicon polymer is set so that a polymer coating of 40 to 45 μmthickness results.

Embodiment 2

A large-area radiator of 320×360 mm size is to be provided with a achemically tempered front pane of 1.1 mm thickness. Glass D263, forexample DESAG AG of Grünenplan, is used for the front pane. 1.1 mm thickpanes made of this glass are dipped for 16 h in a hot KNO₃ bath at 450°C. in order to temper them by the “Na —K exchange”. By means of this,tempering of more than 230 MPa is created in a surface layer to a depthof 80 μm. It was observed that, in the subsequent processes in thecourse of producing the large-area radiator, a portion of the temperingwas “washed out” again, but tempering of more than 200 MPa was observedto be a permanent value.

Flat Light Source

The invention relates to a large-area radiator with a front pane and arear element, wherein the front pane is kept apart from the rear elementby means of spacer elements, wherein a gaseous filler has beenintroduced into the space between the front pane and the rear elementand is at a lesser pressure than the pressure of the surroundingatmosphere, and wherein the front pane is made of a glass material.

Transmissive LCDs require background illumination by a strong light ofhomogeneous luminance, reduced thickness, low rate of breakage duringassembly and handling, and with a great strength over time. Gasdischarge lamps with a filling of a noble gas at underpressure meet therequirements of homogeneous luminance and low heat emission. These lampscan also be designed as large-area radiators.

The essential mechanical components of such large-area radiators are thefront and rear pane and spacer elements for keeping the front and rearpanes apart. Front and rear panes made of glass are preferred. It isknown to provide rear panes made of glass with reflecting coatings, or

Larger-area radiators are known in the prior art, wherein the dischargecurrent flows through “folded” channels between the front and rearpanes, which requires an operating voltage of several hundred Volts(Company Publication “Flat Candle Backlight Products for 4″ DiagonalLCD”). Large-area radiators are also known, in which the current flowsdirectly from the rear to the front pane. Such large-area radiators areoperated in connection with LCD applications with operating voltages ofonly approximately 10 V.

A considerable disadvantage of large-area radiators with anunderpressure filling is the great thickness and large weight. Thethickness is the result of the minimum discharge distance and of thethickness of the glass panes for the front and rear panes. The panethickness is the result of strength requirements.

Large-area radiators with front and rear panes of approximately 2.5 mmthickness, which are maintained at an essentially even distance of 40 to50 mm by spacer elements, represent the prior art. FIG. 1 shows asection in a perspective view through a known large-area radiator, inwhich the front and rear pane and parallel, continuous, strip-shapedspacer elements can be seen. It has been shown that when employingthinner glass panes for the front and rear pane, for example forweight-saving or for reducing the thickness of the large-area radiator,the following problems occur:

-   -   a too large mechanical stresses in the panes,    -   too great bending of the panes between spacer elements,    -   buckling, tipping over or tearing off of the spacer elements.

The mechanical stresses in the panes because of the exterior pressureare considered to be an essential problem. The tensile stress at theexterior surfaces of the pane is on a scale of approximately σ×a(w/t)²,wherein t identifies the pane thickness and w the distance between thespacer elements. It can be seen that when the pane thickness is reduced,it is also necessary to reduce the distance between the spacer elements.It is assumed that with a pane thickness t=2.5 mm, a distance betweenthe spacer elements of at least w=40 to 50 mm is required to keep thetensile stress at the exterior surface of the panes below approximately10 MPa (expected fatigue strength of class). At a pane thickness of 1mm, a distance between the spacer elements of less than 20 mm wouldtherefore be required. This results in an increased production outlayand a reduction of the light yield because of the many spacer elements.This assumption has up to now prevented the production of large-arearadiators with thinner front and rear panes, or with a greater distancebetween the spacer elements.

It is the object of the invention to achieve a weight reduction of alarge-area radiator of the type mentioned at the outset.

This object of the invention is attained in that the front pane and/orthe rear pane are embodied as glass panes, which are at least partiallythermally or chemically tempered.

By means of thermally or chemically tempered glass panes it is possibleto achieve considerably greater spacer element distances than with knownlarge-area radiators. Table 1 shows what maximum distance can beobtained for the spacer elements w as a function of the pane thicknesst, and what surface pressure tempering must be achieved in the glasspanes at least (σ_(vtmin)).

TABLE 1 without coating with coating t (mm) w (mm) σ_(v1min) (MPa)W_(max) (mm) σ_(v1min) (MPa) 2.1 105 120 120 120 1.9 85 100 100 100 1.768 80 82 80 1.5 52 60 65 60

Tempering of more than 100 MPa in thin glass panes can only be achievedwith high-stress glass (thermal expansion coefficient_(σ20,300)>7×10⁻⁶1/° C.) or with glass with a high T_(G)(T_(G)>550° C.;T_(G) is the temperature at which the viscosity of the glass is10^(13.6) dPa). The use of glass with a high T_(G) has the furtheradvantage that it is then possible to subject the large-area radiatorsto high temperatures during the manufacturing process. Therefore glasswith a high T^(G) is preferred. But the thermal tempering of thin glasspanes is still very expensive.

For panes with low stress, or for panes of a thickness of less than 1.5mm, thermal tempering shows hardly positive effects. Therefore chemicaltempering by means of the methods known per se is preferred.

The combination of chemical tempering and coating with ductile polymerlayers here leads to a further increase in strength. Coating must beperformed after tempering.

With chemically tempered glass it is possible to achieve considerablygreater distances between the spacer elements than with the knownlarge-area radiators, along with a sufficient strength of the large-arearadiators. Table 2 shows the distance w between spacer elements whichcan be achieved as a function of the pane thickness t, and what surfacepressure tempering must be achieved in the glass panes at least(σ_(vtmin)).

TABLE 2 without coating with coating t (mm) w (mm) σ_(v1min) (MPa)W_(max) (mm) σ_(v1min) (MPa) 1.5 95 200 105 200 1.3 81 200 89 200 1.1 70200 76 200 0.9 55 200 61 200 0.7 42 180 46 180 0.5 28 160 32 160

It was found that the strength of the large-area radiators can beconsiderably increased if the stability under load of the spacerelements is increased by using wavy spacer elements instead of straightspacer elements.

The object of the invention is also attained in that the front paneand/or the rear element are embodied as glass panes, which are at leastpartially provided with a coating consisting of a ductile polymermaterial.

Large-area radiators with a rectangular base and of even thickness aremade the basis for describing the invention, however, the teaching inaccordance with this invention can also be applied to other shapes oflarge-area radiators. Therefore those are made a part of the invention.

Parallel, strip-like spacer elements, which continuously extend parallelwith an edge of the large-area radiator, are made the basis fordescribing the invention. However, the teaching in accordance with thisinvention can also be applied to any other designs, in particularsegmented spacer elements (FIG. 3), and spot spacer elements (FIG. 4),or wavy spacer elements (FIG. 5). Therefore those are made a part of theinvention.

It was discovered that a sufficient strength of large-area radiatorscould also be achieved with front and rear panes of glass of a thicknessof less than 2.5 mm, if the glass panes are laminated with plasticcoatings.

Tests have shown that by means of laminating the exterior of the glasspanes used as front and rear panes with thin, ductile polymer films asufficient surface strength of the large-area radiators is achieved.Suitable for this are thin coatings of silicon, polyurethane or polymersfrom the group of ormoceres. Because of their high temperatureresistance (up to 200° C.) and great resistance to many organic solventsand aqueous solutions, silicon coatings are preferred.

The polymer films already become effective at coating thicknessesstarting at approximately 6 μm. The stability-increasing effects of thecoatings basically increase with increasing thickness. However, startingat a thickness of 50 μm this increase is no longer significant. Thethickness range between 6 to 50 μm is preferred, because then theelasticity of the bond is little reduced and the shrinkage of thepolymer films leads to only small stresses in the glass panes. However,the application of thicker coatings up to approximately 200 μm can beuseful for manufacturing reasons.

It is additionally possible to employ primers for improving theadherence of the mainly homopolar polymers on the polar glass surfacewhich, by a reactive bond of OH groups on the glass surface with theirhomopolar side chains, provide a homopolar glass surface with goodadhesive properties for homopolar organic polymers. Dimethoxydimethyxsilane or hexamethyl disilazane, for example, are suitable primers.

The stability-increasing effect of the polymer coatings actually is astability conservation. The coatings prevent the creation ofstability-reducing micro-defects in the surface of the glass panesduring transport, assembly or handling of the glass panes. This effecttherefore is particularly developed when the coatings are applied early,preferably immediately following the drawing of the glass panes, andeven more preferred prior to cutting the glass panes (for example forfabricating the panes in the size of large-area radiators).

By means of the above described glass panes it is possible to achieveconsiderably greater distances between spacer elements than with theknown large-area radiators, without their strength being reduced. Table3 shows by way of example what distances w between spacer elements canbe achieved as a function of the pane thickness t.

TABLE 3 t (mm) w (mm) 2.1 75 1.9 65 1.7 54 1.5 48 1.3 37 1.1 31 0.9 250.7 20

An advantageous variation can result if the polymer coating is appliedat a temperature which lies above the operating temperature of thelarge-area radiator. By means of this it is achieved that the polymercoating on the pane is under permanent compressive strain and istherefore scratch-proof.

Coatings with polymers have the disadvantage that the coated glass panesmay not be exposed to high temperatures in the course of subsequentthermal treatment. The temperature must remain clearly below 200° C. asa rule. This limitation is unacceptable if, for example, the panes mustbe soldered in the course of mounting the large-area radiator, or ifgettering must be performed on mounted large-area radiators.

In this case it is possible to make use of the advantages of theinvention by sealing the panes with a removable protective filmimmediately following their production. This temporary protective filmis washed off prior to the respective temperature treatment. Thereafter,another temporary sealing takes place, if required, or the immediateapplication of the permanent coatings in accordance with the invention.

Tests show that it is possible to create a thermal tempering of panesstarting from a thickness of 1.5 mm by strongly blowing cold air againstthem or dipping them into oil, or oil-covered water, which considerablyincreases the stability of the large-area radiators. Thermal temperingshould take place after cutting the glass panes (for example forfabricating the panes in the size of large-area radiators).

The combination of thermal tempering and coating with ductile polymerlayers results in a further increase of stability. Coating must takeplace after tempering.

The invention will be explained in greater detail in what follows bymeans of two exemplary embodiments:

Exemplary Embodiment 1

The rear pane of a large-area radiator, which itself is already finishedand capable of functioning, is sprayed with a thin coat of atwo-component silicon polymer after the last baking process, so that acontinuous wetting layer is created. The layer is then polymerized. Theamount of silicon polymer is set in such a way that a polymer coating of40 to 45 μm thickness results.

Exemplary Embodiment 2

A large-area radiator of 320×360 mm size is to be provided with achemically tempered front pane of 1.1 mm thickness. Glass D263(reference: DESAG AG of Grünenplan) is used for the front pane. 1.1 mmthick panes made of this glass are dipped for 16 h in a hot KNO₃ bath at450° C. in order to temper them by the “Na —K exchange”. By means ofthis, tempering of more than 230 MPa is created in a surface layer to adepth of 80 μm. It was observed that, in the subsequent processes in thecourse of producing the large-area radiator, a portion of the temperingwas “washed out” again, but tempering of more than 200 MPa was observedto be a permanent value.

1. In a large-area radiator of homogeneous luminance with a front paneand a rear element, wherein spacer elements extending from the frontpane to the rear element include one end in contact with the front paneand an opposing end in contact with the rear element to keep the frontpane apart from the rear element, a gaseous filler is introduced into aspace between the front pane and the rear element and is at a lesserpressure than a pressure of a surrounding atmosphere, and the front paneis made of a glass material, the improvement comprising: at least one ofthe front pane and the rear element at least partially of one of athermally tempered glass pane and a chemically tempered glass pane;wherein at least one of a measurement of a wall thickness of at leastone of the front pane and the rear element is 0.5 mm to 2.1 mm, and istempered by a chemical tempering of more than 160 MPa.
 2. In alarge-area radiator of homogeneous luminance with a front pane and arear element, wherein spacer elements extending from the front pane tothe rear element include one end in contact with the front pane and anopposing end in contact with the rear element to keep the front paneapart from the rear element, a gaseous filler is introduced into a spacebetween the front pane and the rear element and is at a lesser pressurethan a pressure of a surrounding atmosphere, and the front pane is madeof a glass material, the improvement comprising: at least one of thefront pane and the rear element each embodied as a glass pane which atleast partially has a coating of a ductile polymer material, wherein atleast one of a measurement of a wall thickness of at least one of thefront pane and the rear element is less than 2.1 mm.
 3. In thelarge-area radiator in accordance with claim 2, wherein the coating is afilm including one of a silicon, a polyurethane and a polymer material,selected from a group of ormoceres.
 4. In the large-area radiator inaccordance with claim 3, wherein the coating has a thickness of morethan 6 μm.
 5. In the large-area radiator in accordance with claim 4,wherein the thickness of the coating is within a range of 6 μm and 50μm.
 6. In the large-area structure in accordance with claim 5, wherein aprimer is used for bonding the coating to a surface of the glass pane,and the primer is one of a dimethoxydimethyl silane and a hexamethyldisilazane.
 7. In the large-area radiator in accordance with claim 6,wherein the glass pane is at least partially tempered one of thermallyand chemically.
 8. In the large-area radiator in accordance with claim7, wherein the spacer elements are wavy and are arranged between thefront pane and the rear element, wherein a wavy line extends generallyparallel with a planar extension of the front pane.
 9. In the large-arearadiator in accordance with claim 2, wherein the coating has a thicknessof more than 6 μm.
 10. In the large-area structure in accordance withclaim 2, wherein a primer is used for bonding the coating to a surfaceof the glass pane, and the primer is one of a dimethoxydimethyl silaneand a hexamethyl disilazane.
 11. In the large-area radiator inaccordance with claim 2, wherein the glass pane is at least partiallytempered one of thermally and chemically.
 12. In a large-area radiatorof homogeneous luminance with a front pane and a rear element, whereinspacer elements extending from the front pane to the rear elementinclude one end in contact with the front pane and an opposing end incontact with the rear element to keep the front pane apart from the rearelement, a gaseous filler is introduced into a space between the frontpane and the rear element and is at a lesser pressure than a pressure ofa surrounding atmosphere, and the front pane is made of a glassmaterial, the improvement comprising: at least one of the front pane andthe rear element at least partially of one of a thermally tempered glasspane and a chemically tempered glass pane; wherein at least one of ameasurement of a wall thickness of at least one of the front pane andthe rear element is 1.5 mm to 2.1 mm and a thermal tempering is greaterthan or equal to 60 Mpa.
 13. In the large-area radiator in accordancewith claim 12, wherein a temperature at which a viscosity of the glassmaterial of at least one of the front pane and the rear element is 13.6dPas (TG temperature) is greater than 550°.
 14. In the large-arearadiator in accordance with claim 12, wherein the spacer elements arewavy and are arranged between the front pane and the rear element,wherein a wavy line extends generally parallel with a planar extensionof the front pane.